Conformational Control of Tetrahydropyran-Based Hybrid Dipeptide Catalysts Improves Activity and Stereoselectivity

Herein, we introduce and demonstrate how carbohydrates can be used as conformational control units of organocatalysts to tune their catalytic properties. New hybrid dipeptide-like organocatalysts based on ζ-sugar aminoacids and proline were prepared and tested for the asymmetric Michael addition of aldehydes to β-nitrostyrenes. Taking full advantage of the modular nature of the carbohydrate motif, both reactivity and stereoselectivity were significantly improved. By simple structural changes, such as the elimination of the methoxy group in the C4 position of the tetrahydropyran ring, we obtained two complementary catalysts that allow access to both enantiomers of the γ-nitroaldehydes with excellent yields, diastereoselectivity, and enantiomeric excesses between 97 and 99%, using a catalytic load even below 1 mol%.This research was supported by the Spanish MINECO (CTQ2014‐59649‐P), cofinanced by the European Regional Development Fund (ERDF) and the Canary Islands Government (ProID2017010019, ACIISI/FEDER, UE). The authors thank technician Ms. Estefanía Gámez García for her experimental assistance. J. B.‐G. thanks the Spanish MEC for an FPU fellowship.Peer Reviewe